Substituted anthranilic acid derivatives are useful intermediates in the manufacturing of a variety of chemical products including agricultural chemicals; see, for example, U.S. Pat. No. 4,954,163.
The direct electrophilic substitution of anthranilates to 3- and/or 5-substituted analogs is often not very successful because of the mixtures produced. Chlorination of methyl anthranilate, for example, gives mixtures of 5-chloroanthranilate and 3-chloroanthranilate along with substantial amounts of dichlorination. ##STR1##
Because of the unpredictability with respect to electrophilic substitutions, other approaches to substituted anthranilates are usually advocated. For example, U.S. Pat. No. 4,306,074 discloses the preparation of a mixture of alkyl 3-chloroanthranilate and alkyl 6-chloroanthranilate in a 3:1 ratio from 3-chlorophthalic anhydride by amination, Hofmann degradation and esterification. ##STR2## Despite three discrete steps, a mixture is still produced.
In U.S. Pat. No. 4,310,677, alkyl anthranilates are prepared by reacting an isatin with an alcohol and hydrogen peroxide in the presence of an alkali metal alkoxide. ##STR3## However, the isatins required for this approach are often very difficult to prepare.
Therefore, it is desirable to have a process for preparing anthranilic acids, particularly 3- and/or 5-substituted anthranilic acids, in good yield and free of isomeric byproducts from readily available starting materials.